Aerodynamically efficient lightweight vertical take-off and landing aircraft with pivoting rotors and stowing rotor blades

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation of U.S. patent application Ser. No. 14/218,845 to Bevirt et al., filed Mar. 18, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND

0002Field of the Invention

0003This invention relates to powered flight, and more specifically to a vertical take-off and landing aircraft with pivoting rotors and stowing rotor blades.

0004Description of Related Art

0005There are generally three types of vertical takeoff and landing (VTOL) configurations: wing type configurations having a fuselage with rotatable wings and engines or fixed wings with vectored thrust engines for vertical and horizontal translational flight; helicopter type configuration having a fuselage with a rotor mounted above which provides lift and thrust; and ducted type configurations having a fuselage with a ducted rotor system which provides translational flight as well as vertical takeoff and landing capabilities.

0006The amount of thrust required to take-off in a vertical take-off scenario greatly exceeds the thrust needed to keep the same vehicle aloft during forward flight, when the wings are providing lift. The amount of thrust required to transition from a vertical take-off mode to horizontal, forward, flight mode may also be quite high. Thus, there may be a mismatch between the power requirements if there are not possibilities to change power delivery paradigms during flight.

0007In order to provide efficiency in both vertical take-off and forward flight modes, improvements to past systems must be made. What is called for is a vertical take-off and landing aircraft that incorporates efficiencies into all use modes.

SUMMARY

0008An aerial vehicle adapted for vertical takeoff and landing using a set of wing mounted thrust producing elements and a set of tail mounted rotors for takeoff and landing. An aerial vehicle which is adapted to vertical takeoff with the rotors in a rotated, take-off attitude then transitions to a horizontal flight path, with the rotors rotated to a typical horizontal configuration. The aerial vehicle uses different configurations of its wing mounted rotors and propellers to reduce drag in all flight modes.

BRIEF DESCRIPTION OF THE DRAWINGS

0009<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of an aerial vehicle in forward flight according to a first embodiment of the present invention.

0010<figref idref="DRAWINGS">FIG. 2</figref> is a side view of an aerial vehicle in a forward flight configuration according to a first embodiment of the present invention.

0011<figref idref="DRAWINGS">FIG. 3</figref> is a top view of an aerial vehicle in a forward flight configuration according to a first embodiment of the present invention.

0012<figref idref="DRAWINGS">FIG. 4</figref> is a front view of an aerial vehicle in a forward flight configuration according to a first embodiment of the present invention.

0013<figref idref="DRAWINGS">FIG. 5</figref> is a perspective view of an aerial vehicle in takeoff configuration according to a first embodiment of the present invention.

0014<figref idref="DRAWINGS">FIG. 6</figref> is a front view of an aerial vehicle in takeoff configuration according to a first embodiment of the present invention.

0015<figref idref="DRAWINGS">FIG. 7</figref> is a side view of an aerial vehicle in takeoff configuration according to a first embodiment of the present invention.

0016<figref idref="DRAWINGS">FIG. 8</figref> is a perspective view of an aerial vehicle in a transition configuration according to a first embodiment of the present invention.

0017<figref idref="DRAWINGS">FIG. 9</figref> is a sequence of views illustrating transition of the wing according to a first embodiment of the present invention.

0018<figref idref="DRAWINGS">FIG. 10</figref> is a perspective view of an aerial vehicle in forward flight with wing rotor blades stowed according to a first embodiment of the present invention.

0019<figref idref="DRAWINGS">FIG. 11</figref> is a front view of an aerial vehicle in a forward flight configuration with wing rotor blades stowed according to a first embodiment of the present invention.

0020<figref idref="DRAWINGS">FIG. 12</figref> is a top view of an aerial vehicle in a forward flight configuration with wing rotor blades stowed according to a first embodiment of the present invention.

0021<figref idref="DRAWINGS">FIG. 13</figref> is a side view of an aerial vehicle in a forward flight configuration with wing rotor blades stowed according to a first embodiment of the present invention.

0022<figref idref="DRAWINGS">FIG. 14</figref> is a perspective view of a wing rotor with the front cover removed for clarity according to some embodiments of the present invention.

0023<figref idref="DRAWINGS">FIG. 15</figref> is a front view of a wing rotor with the front cover removed for clarity according to some embodiments of the present invention.

0024<figref idref="DRAWINGS">FIG. 16</figref> is a side view of a wing rotor with its blades deployed according to some embodiments of the present invention.

0025<figref idref="DRAWINGS">FIG. 17</figref> is a side view of a wing rotor with its blades stowing according to some embodiments of the present invention.

0026<figref idref="DRAWINGS">FIG. 18</figref> is a side view of a wing rotor with its blades stowing according to some embodiments of the present invention.

0027<figref idref="DRAWINGS">FIG. 19</figref> is a side view of a wing rotor with its blades stowing according to some embodiments of the present invention.

0028<figref idref="DRAWINGS">FIG. 20</figref> is a side view of a wing rotor with its blades stowed according to some embodiments of the present invention.

0029<figref idref="DRAWINGS">FIG. 21</figref> is a perspective view of a tail rotor according to some embodiments of the present invention.

0030<figref idref="DRAWINGS">FIG. 22</figref> is a side view of a tail rotor in a forward flight configuration according to some embodiments of the present invention.

0031<figref idref="DRAWINGS">FIG. 23</figref> is a side view of a tail rotor in a take-off configuration to some embodiments of the present invention.

0032<figref idref="DRAWINGS">FIG. 24</figref> is a side view of a tail rotor and its deployment mechanism in a stowed configuration according to some embodiments of the present invention.

0033<figref idref="DRAWINGS">FIG. 25</figref> is a side view of a tail rotor and its deployment mechanism moving from a stowed configuration according to some embodiments of the present invention.

0034<figref idref="DRAWINGS">FIG. 26</figref> is a side view of a tail rotor and its deployment mechanism moving from a stowed configuration according to some embodiments of the present invention.

0035<figref idref="DRAWINGS">FIG. 27</figref> is a side view of a tail rotor and its deployment mechanism in a deployed configuration according to some embodiments of the present invention.

0036<figref idref="DRAWINGS">FIG. 28</figref> is a front view of a tail rotor and its deployment mechanism in a deployed configuration according to some embodiments of the present invention.

0037<figref idref="DRAWINGS">FIG. 29</figref> is a perspective view of an aerial vehicle in take-off configuration according to a second embodiment of the present invention.

0038<figref idref="DRAWINGS">FIG. 30</figref> is a front view of an aerial vehicle in take-off configuration according to a second embodiment of the present invention.

0039<figref idref="DRAWINGS">FIG. 31</figref> is a side view of an aerial vehicle in take-off configuration according to a second embodiment of the present invention.

0040<figref idref="DRAWINGS">FIG. 32</figref> is a top view of an aerial vehicle in take-off configuration according to a second embodiment of the present invention.

0041<figref idref="DRAWINGS">FIG. 33</figref> is a perspective view of an aerial vehicle in a forward flight configuration according to a second embodiment of the present invention.

0042<figref idref="DRAWINGS">FIG. 34</figref> is a front view of an aerial vehicle in a forward flight configuration according to a second embodiment of the present invention.

0043<figref idref="DRAWINGS">FIG. 35</figref> is a side view of an aerial vehicle in a forward flight configuration according to a second embodiment of the present invention.

0044<figref idref="DRAWINGS">FIG. 36</figref> is a top view of an aerial vehicle in a forward configuration according to a second embodiment of the present invention.

0045<figref idref="DRAWINGS">FIG. 37</figref> is a side view illustrating nested blades according to some embodiments of the present invention.

0046<figref idref="DRAWINGS">FIG. 38</figref> is a side view of a deployed rotor unit with rotor blades extended according to some embodiments of the present invention.

0047<figref idref="DRAWINGS">FIG. 39</figref> is a side view of rotor unit with two blade sets in a forward flight mode according to some embodiments of the present invention.

0048<figref idref="DRAWINGS">FIG. 40</figref> is a side view of rotor unit with two blade sets in a take-off mode according to some embodiments of the present invention.

0049<figref idref="DRAWINGS">FIG. 41</figref> is a front view of an electric motor according to some embodiments of the present invention.

0050<figref idref="DRAWINGS">FIG. 42</figref> is a partial view of a directional clutch in an electric motor according to some embodiments of the present invention.

0051<figref idref="DRAWINGS">FIG. 43</figref> is a partial view of a directional clutch in an electric motor according to some embodiments of the present invention.

0052<figref idref="DRAWINGS">FIG. 44</figref> is a partial cross-sectional view of directional clutches in an electric motor according to some embodiments of the present invention.

0053<figref idref="DRAWINGS">FIG. 45</figref> is a perspective view of an aerial vehicle in take-off configuration according to a third embodiment of the present invention.

0054<figref idref="DRAWINGS">FIG. 46</figref> is a front view of an aerial vehicle in take-off configuration according to a third embodiment of the present invention.

0055<figref idref="DRAWINGS">FIG. 47</figref> is a top view of an aerial vehicle in take-off configuration according to a third embodiment of the present invention.

0056<figref idref="DRAWINGS">FIG. 48</figref> is a side view of an aerial vehicle in take-off configuration according to a third embodiment of the present invention.

0057<figref idref="DRAWINGS">FIG. 49</figref> is a perspective view of an aerial vehicle according to a fourth embodiment of the present invention.

0058<figref idref="DRAWINGS">FIG. 50</figref> is a front view of an aerial vehicle in a take-off configuration according to a fourth embodiment of the present invention.

0059<figref idref="DRAWINGS">FIG. 51</figref> is a top view of an aerial vehicle in a take-off configuration according to a fourth embodiment of the present invention.

0060<figref idref="DRAWINGS">FIG. 52</figref> is a side view of an aerial vehicle in a take-off configuration according to a fourth embodiment of the present invention.

0061<figref idref="DRAWINGS">FIG. 53</figref> is a perspective view of an aerial vehicle in a forward flight configuration according to a fourth embodiment of the present invention.

0062<figref idref="DRAWINGS">FIG. 54</figref> is a top view of an aerial vehicle in a forward flight configuration according to a fourth embodiment of the present invention.

0063<figref idref="DRAWINGS">FIG. 55</figref> is a front view of an aerial vehicle in a forward flight configuration according to a fourth embodiment of the present invention.

0064<figref idref="DRAWINGS">FIG. 56</figref> is a side view of an aerial vehicle in a forward flight configuration according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION

0065Although vertical takeoff and landing (VTOL) aircraft have always been desired, compromises in the realization of these aircraft have limited their usefulness and adoption to certain niches. The thrust needed for VTOL is significantly higher than the thrust needed to maintain horizontal flight. The vertical take-off thrust may also be needed during the transition to forward flight. Once moving in forward flight, the wings of the aircraft provide lift, supplanting a function delivered by motors during VTOL and during transition. Thrust producing elements needed during take-off, but not during forward flight, may be altered during forward flight such that they impart less drag onto the flying system.

0066In some aspects, an aerial vehicle may use bladed propellers powered by electric motors to provide thrust during take-off. The propeller/motor units may be referred to as rotor assemblies. In some aspects, the wings of the aerial vehicle may rotate, with the leading edges facing upwards, such that the propellers provide vertical thrust for take-off and landing. In some aspects, the motor driven propeller units on the wings may themselves rotate relative to a fixed wing, such that the propellers provide vertical thrust for take-off and landing. The rotation of the motor driven propeller units may allow for directional change of thrust by rotating both the propeller and the electric motor, thus not requiring any gimbaling, or other method, of torque drive around or through a rotating joint.

0067In some aspects, some or all of the wing mounted motor driven rotors are adapted to have the rotor blades fold back into a stowed position wherein the blades nest in recesses in the adjoining nacelle body after a transition to horizontal flight. The nested blades may result in a significantly lower drag of the aerial vehicle, while also allowing a significantly reduced power usage with only some of the rotors providing forward thrust.

0068In some aspects, extended nacelles with two coaxial propellers are used such that one of the propellers is used during forward flight, and another during vertical take-off and landing. The VTOL propeller may be adapted to nest its blades during forward flight. In some aspects, the extended nacelle may reside at the tip of a wing, or at the end of a rear V-tail element, and be adapted to rotate such that the VTOL propeller may provide vertical thrust during take-off and landing. In some aspects, each of the coaxial propellers has its own electric motor. In some aspects, the coaxial propellers are driven by the same electric motor. In some aspects, the electric motor has directional clutches such that one propeller is driven while the motor rotates in a first direction, and the other propeller is driven while the motor rotates in a second direction.

0069In some aspects, the motor driven rotors attached to the wing are adapted to place the mass of the motor and rotor significantly forward of the wing. In some aspects, this forward location allows for the rotation of the rotors to a vertical thrust orientation that has the airflow predominantly in front of the leading edge of the wing, reducing air flow impingement by the wing during VTOL operations. In some aspects, this forward location of the mass of the rotors and motors allows for unusual wing configurations, such as swept forward wings, whose otherwise possible drawbacks during higher g-force maneuvers are partially or fully moderated by this mass placement.

0070In some aspects, the mass balance of the aerial vehicle may be altered by movement of masses such as the battery mass. In some aspects, the battery mass may be adjusted to retain balance when a single vs. a multi-passenger load is supported. In some aspects, mass balance may be adjusted in automatic response to sensors within the aerial vehicle. In some aspects, the battery mass may be distributed between a two or more battery packs. The battery packs may be mounted such that their position may be changed during flight in response to changes in the balance of the aerial vehicle. In some aspects, the flight control system of the aerial vehicle may sense differential thrust requirements during vertical take-off and landing, and may move the battery mass in order to achieve a more balanced thrust distribution across the rotor assemblies. In some aspects, the battery mass may be moved should there be a failure of a rotor assembly during transition or vertical take-off and landing, again to balance the thrust demands of the various remaining functioning rotors.

0071In a first embodiment of the present invention, as seen in <figref idref="DRAWINGS">FIGS. 1-4</figref>, an aerial vehicle <b>100</b> is seen in first forward flight configuration, as would be seen just after having transitioned from a vertical take-off configuration. In another forward flight mode, the blades of the wing mounted rotors will stow and nest, as discussed below. The aircraft body <b>101</b> supports a left wing <b>102</b> and a right wing <b>103</b>. Motor driven rotor units <b>106</b> include propellers <b>107</b> which may stow and nest into the nacelle body. The aircraft body <b>101</b> extends rearward is also attached to raised rear stabilizers <b>104</b>. The rear stabilizers have rear motors <b>105</b> attached thereto. In some aspects, the rear motors may also have front hubs, or spinners, which are omitted from some Figures for illustrative purposes.

0072As seen in top view in <figref idref="DRAWINGS">FIG. 3</figref>, the wings <b>102</b>, <b>103</b> are partially swept forward. Aerial vehicles according to embodiments of the present invention may include partially or wholly forward swept wings with spanwise distributed masses located forward of the leading edge. The divergent aeroelastic torsion commonly seen in forward-swept wing designs is substantially reduced by the presence of the masses cantilevered forward of the wing, which create opposing torque. As seen in <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, the wing rotor assemblies <b>106</b> are mounted forward of the wing leading edge, and are also then forward of the neutral axis of the wing.

0073<figref idref="DRAWINGS">FIGS. 5-7</figref> illustrate the aerial vehicle <b>100</b> in a vertical take-off and landing configuration such that the thrust of the rotors is directed upward. The wing <b>102</b>, <b>103</b> have been rotated relative to the body <b>101</b> around a pivot <b>108</b>. In some embodiments, the wings are fixed to each other with structure that crosses through the vehicle body <b>101</b>. As seen in side view in <figref idref="DRAWINGS">FIG. 7</figref>, whereas the wing rotors <b>107</b> have had their thrust redirected for vertical take-off due to the rotation of the wing, the rear rotors <b>105</b> have had their thrust redirected due to their rotation relative to the rear stabilizers <b>104</b>. Although referred to above as a pivot, the attachment of the wing to the aerial vehicle body may use a linkage adapted to maintain a forward position of the mass of the wing and rotor assemblies.

0074<figref idref="DRAWINGS">FIGS. 21-28</figref> illustrate the configurations of the rear rotor. The deployment of a rear rotor from a stowed, forward flight, configuration to a deployed, vertical take-off, position, as well as a variety of intervening positions, may be achieved using a deployment mechanism which rotates the rotor relative to the rear stabilizers. <figref idref="DRAWINGS">FIG. 22</figref> illustrates a stowed, forward flight, configuration of rear rotor unit <b>105</b>. The rear nacelle portion <b>115</b> may be rigidly mounted to a rear stabilizer in some embodiments. The spinner <b>114</b> and the motor cover <b>113</b> provide aerodynamic surfaces for the front portion of the nacelle. The propeller <b>111</b> extends through the spinner <b>114</b>. In a fully deployed position, as seen in <figref idref="DRAWINGS">FIG. 23</figref>, and in a partial front view in <figref idref="DRAWINGS">FIG. 28</figref>, the motor <b>110</b>, motor cover <b>113</b>, spinner <b>114</b>, and propeller <b>111</b> have rotated to a position adapted to provide vertical thrust. The electric motor/propeller combination being on the outboard side of the articulating joint allows for a rigid mounting of the propeller to the motor, which is maintained even as the propeller is moved through various attitudes relative to the rear nacelle portion. With such a configuration the rotating power from the motor need not be gimbaled or otherwise transferred across a rotating joint.

0075<figref idref="DRAWINGS">FIGS. 24-27</figref> illustrate a sequence of positions of the motor and propeller relative to the rear nacelle, also to the rear tail structure of the aerial vehicle. As the articulating portion of the rear rotor unit begins its deployment, it can be seen in <figref idref="DRAWINGS">FIG. 25</figref> that the linkages first deploy the articulating portion forward, as opposed to merely pivoting around a single pivot point. The multi-bar linkage allows for the use of a single actuator for this complex deployment. <figref idref="DRAWINGS">FIG. 26</figref> illustrates the rear rotor unit as it does rise above the top of the rear nacelle, and achieves full deployment as seen in <figref idref="DRAWINGS">FIG. 27</figref>. With the multi-bar linkage the motion of the articulating portion, which includes the motor, propeller, and spinner, is almost horizontal at the position of full deployment. As the thrust direction of the rotor is vertical in the fully deployed position, the actuator powering the deployment of the multi-bar linkage is not required to offset, or counteract, the thrust of the rotor.

0076<figref idref="DRAWINGS">FIG. 9</figref> illustrates various positions of the wing and rear rotors as would be seen during transition from take-off to forward flight mode, or from forward flight mode to vertical take-off and landing mode. After a vertical take-off, the rotors transition from a configuration providing vertical thrust through positions rotating towards the horizontal. As the forward speed of the aerial vehicle increases, the wings begin to generate lift such that not as much vertical thrust is needed to maintain altitude. With sufficient forward speed, lift is maintained by the wings and the thrust needed for forward flight is able to be provided by fewer rotors. In some aspects, the wings are raised to a vertical take-off configuration with the use of a linkage adapted to slide the wing pivot forward as the wing reaches deployment. This allows for a more favorable compromise in center of gravity location between VTOL and forward flight modes by locating the wing-mounted rotor assemblies farther forward in the VTOL configuration.

0077<figref idref="DRAWINGS">FIGS. 10-13</figref> illustrate a forward flight configuration of the aerial vehicle <b>100</b> according to some embodiment of the present invention. The propeller blades of the wing mounted rotors <b>106</b> have been stowed and are nested within recesses along the nacelle. As forward flight requires significantly less thrust than required for vertical take-off, many of the individual motors and rotors may be deactivated during forward flight. To reduce drag, the blades may be folded back into a stowed position. To further reduce drag, the nacelles may have recesses such that the folded blades are adapted to nest within the recesses, creating a very low drag nacelle during forward flight. The rear rotors <b>105</b> may be used to provide forward thrust during this forward flight configuration.

0078<figref idref="DRAWINGS">FIG. 14</figref> illustrates a front set of views of a stowing blade set as it stows from a fully deployed configuration to a fully stowed configuration. The blades nest into recesses along the nacelle such that the stowed blade set gives the effective wetted area of a simple nacelle. <figref idref="DRAWINGS">FIG. 15</figref> illustrates a wing mounted rotor unit according to some embodiments as it stows from a fully deployed configuration to a stowed configuration. Of note is that the rotor assembly, which may comprise an electric motor, the blade set, and the spinner, may itself deploy as a whole as seen in <figref idref="DRAWINGS">FIG. 38</figref>, for example. In some aspects, the deployment of the rotor assembly utilizes a linkage, such as the linkage <b>209</b> of <figref idref="DRAWINGS">FIG. 38</figref>, which deploys the rotor to a vertical position while simultaneously pushing it forward and away from the remaining body of the nacelle. The push away from the remaining body of the nacelle reduces the download in the wing from the downwash of the associated rotor.

0079<figref idref="DRAWINGS">FIGS. 16-20</figref> illustrate a sequence of positions as the blades <b>107</b> of a wing mounted rotor <b>106</b> fold down into a stowed position. <figref idref="DRAWINGS">FIG. 16</figref> illustrates the propeller blades <b>107</b> fully deployed, as would be used in vertical take-off and landing, and during transition to horizontal, forward, flight. Thus succeeding figures illustrate the blades <b>107</b> folding down to a stowed position. As seen in <figref idref="DRAWINGS">FIG. 20</figref>, the blades <b>107</b> fit within recesses <b>116</b> in the nacelle resulting in a low drag configuration <b>117</b>.

0080In an exemplary configuration of the first embodiment, the aerial vehicle has 8 rotors and weighs 900 kg. The rotor diameters are 1.3 meters, with a thrust per rotor of 1100 N. The continuous rpm of the motor at sea level is 1570 rpm, with a maximum of 1920 rpm. The wingspan is 8.5 meters. The battery mass is 320 kg, and the mass per motor is 20 kg. The cruise speed is 320 km/h. The continuous hover shaft power per motor is 29 kW.

0081In a second embodiment of the present invention, as seen in a vertical take-off configuration in <figref idref="DRAWINGS">FIGS. 29-32</figref>, an aerial vehicle <b>200</b> uses forward swept fixed wings <b>202</b>, <b>203</b> with rotors of different types adapted for both vertical take-off and landing and for forward flight. The aircraft body <b>201</b> supports a left wing <b>202</b> and a right wing <b>203</b>. Motor driven rotor assemblies <b>206</b>, <b>207</b> on the wings include propellers which may stow and nest into the nacelle body. The aircraft body <b>201</b> extends rearward is also attached to raised rear stabilizers <b>204</b>. The rear stabilizers have rear rotor assemblies <b>205</b>, <b>208</b> attached thereto. The aerial vehicle <b>200</b> is seen with two passenger seats side by side, as well as landing gear under the body <b>201</b>. Although two passenger seats are illustrated, other numbers of passengers may be accommodated in differing embodiments of the present invention.

0082As seen in top view in <figref idref="DRAWINGS">FIG. 32</figref>, the wings <b>202</b>, <b>203</b> are swept forward. Aerial vehicles according to embodiments of the present invention may include partially or wholly forward swept wings with spanwise distributed masses located forward of the leading edge. The divergent aeroelastic torsion commonly seen in forward-swept wing designs is substantially reduced by the presence of the masses cantilevered forward of the wing, which create opposing torque. Also seen in the top view of <figref idref="DRAWINGS">FIG. 32</figref> is that the propellers of the wing mounted motor driven rotor units are extended forward with, and from, their nacelles such that the air flow in vertical take-off mode is not substantially interfered with by the wings. Similarly, the propellers of the rear stabilizer mounted motor driven rotor units are extended forward with, and from, their nacelles such that the air flow in vertical take-off mode is not substantially interfered with by the rear stabilizers. An illustration of the linkage that may be used to extend the rotors in the vertical configuration may be seen in <figref idref="DRAWINGS">FIG. 38</figref>.

0083Another aspect of the forward swept wing configuration is that it allows for the wings <b>202</b>, <b>203</b> to be mounted to the body <b>201</b> somewhat rearward of where they may have attached otherwise. The rearward attachment allows for a spar connecting the wings to traverse the interior of the aerial vehicle body to the rear of the passenger seats. A further aspect of the forward swept wing with articulating rotors in VTOL mode is the forward stagger of the vertical rotors, which improves longitudinal control authority in vertical and transitional flight for a given wing root location by lengthening the moment arm of these rotors about the center of gravity. This is especially helpful in the case of a failure in one of the rear mounted rotors during VTOL modes. Additionally, the more even longitudinal rotor distribution effected by this configuration reduces the highest torque of the motors required to maintain level vertical flight in worst-case single motor or rotor failure eventuality, allowing the motor size to be reduced.

0084In some aspects, a portion of the wing mounted rotors may be adapted to be used in a forward flight configuration, while other wing mounted rotors may be adapted to be fully stowed during regular, forward, flight. The aerial vehicle <b>200</b> may have four rotors on the right wing <b>203</b> and four rotors on the left wing <b>202</b>. Three of the rotor assemblies on each wing may have wing mounted rotors <b>206</b> that are adapted to flip up into a deployed position for vertical take-off and landing, to be moved back towards a stowed position during transition to forward flight, and then to have their blades stowed, and nested, during forward flight. The fourth rotor assembly <b>207</b> may include a second set of blades to be used for forward flight, as discussed below. Similarly, the each rear stabilizer <b>204</b> may be have two rotor units mounted to it, both of which are adapted to be used during vertical take-off and landing, and transition, modes, but one of which is adapted to be fully stowed as low drag nacelle during forward flight.

0085A multi-modal wing mounted rotor unit <b>207</b> is adapted to use a first set of blades <b>212</b> for forward flight, and a second set of blades <b>213</b> for VTOL and transitional flight modes. The forward flight blades <b>212</b> may be coaxial to the VTOL blades <b>213</b>, and may be attached at different ends of the same nacelle. In the case wherein the VTOL blades are articulated to a vertical position for VTOL flight modes, there may be two motors within the nacelle, one for each blade set. Similarly, a multi-modal rear mounted rotor unit <b>210</b> is adapted to use a first set of blades <b>211</b> for forward flight, and a second set of blades <b>214</b> for VTOL and transitional flight modes. The forward flight blades <b>211</b> may be coaxial to the VTOL blades <b>214</b>, and may be attached at different ends of the same nacelle. In the case wherein the VTOL blades are articulated to a vertical position for VTOL flight modes, there may be two motors within the nacelle, one for each blade set.

0086In some aspects, all of the blades used to provide thrust for VTOL and transitional modes are stowed during forward flight, and different blades are used to provide thrust during forward flight. In some aspects, a single motor is used to provide power for different blade sets depending upon whether VTOL or forward flight modes are being used. In some aspects, two blade sets are placed in a coaxial configuration such that they are supported by a single nacelle, for example.

0087<figref idref="DRAWINGS">FIGS. 33-36</figref> illustrate an aerial vehicle <b>200</b> in a forward flight mode wherein all of the VTOL blades have been stowed, and nested in recesses, such that the nacelles present low drag. In a forward flight mode, the wing mounted rotor units <b>206</b>, <b>207</b> are seen with all of the VTOL blades stowed. Similarly, the rear mounted rotor units <b>205</b>, <b>208</b> also have their VTOL blades stowed. The forward flight blade set <b>211</b> of the multi-modal rear rotor assemblies <b>205</b> and the forward flight blade set <b>212</b> of the multi-modal wing rotor assemblies <b>207</b> are used to provide thrust during forward flight.

0088<figref idref="DRAWINGS">FIGS. 39 and 40</figref> illustrate a motor and rotor unit <b>260</b> adapted to use a first set of blades <b>261</b> for a forward flight mode and a second set of blades <b>263</b> for VTOL and transition modes, in a coaxial configuration that shares a single motor for both blade sets. In this example, both blades are powered by the same electric motor. The electric motor may be adapted with directional clutches such that when the motor is rotated in a first direction the forward flight blades <b>261</b> are engaged, and the VTOL blades <b>263</b> are idled. During forward flight the VTOL blades <b>264</b> may stow and may nest in recesses <b>264</b>. During VTOL and transition modes the motor may rotate in a second direction such that the VTOL blades <b>264</b> are engaged, and the forward flight blades <b>261</b> are disengaged. In the VTOL mode the motor and rotor assembly may be articulated such that the rotors and motor provide vertical thrust, with the entire motor and clutching unit, as well as both sets of blades, outboard of the positioning mechanism, such that no mechanical power related to blade thrust need traverse the gimbaled joint.

0089<figref idref="DRAWINGS">FIGS. 41-44</figref> illustrate a motor <b>265</b> with directional clutches <b>266</b>, <b>267</b> adapted to power a first set of blades when the motor is rotated in a first direction, and to power a second set of blades when the motor is rotated in a second direction. In some aspects, the VTOL blade set and the forward flight blade set may be oriented in different directions such that they both provide thrust in the same direction, although one set is engaged when the motor rotates in a first direction, and the second set is engaged when the motor rotates in a second direction.

0090In a third embodiment of the present invention, as seen in a vertical take-off configuration in <figref idref="DRAWINGS">FIGS. 45-48</figref>, an aerial vehicle <b>300</b> uses forward swept wings <b>302</b>, <b>303</b> with rotors of different types adapted for both vertical take-off and landing and for forward flight. The aircraft body <b>301</b> supports a left wing <b>302</b> and a right wing <b>303</b>. Motor driven rotor assemblies <b>306</b>, <b>307</b> on the wings include propellers which may stow and nest into the nacelle body. The aircraft body <b>301</b> extends rearward and is also attached to raised rear stabilizers <b>304</b>. The rear stabilizers have rear rotor assemblies <b>305</b>, <b>308</b> attached thereto. The aerial vehicle <b>300</b> is adapted for two passenger seats side by side, as well as landing gear under the body <b>301</b>.

0091The wing mounted rotor units <b>306</b>, <b>307</b> are adapted to provide vertical thrust during take-off and landing modes. The inner rotor units <b>306</b> are adapted to deploy to a VTOL configuration using linkages as seen in <figref idref="DRAWINGS">FIG. 38</figref>. The blades of the inner wing rotor units <b>306</b> are adapted to stow when in a forward flight configuration, with the blades nested into recesses in the nacelle. The wing tip rotor units <b>307</b> are adapted to rotate relative to the wing such that the nacelle maintains its shape whether in a VTOL or a forward flight configuration. The VTOL blades <b>313</b> are used for VTOL and transition modes, and the forward flight blades <b>312</b> are used for forward flight, with the VTOL blades stowed and nested. The nacelle that maintains its shape allows for the use of a single motor to power either of the blade sets. The motor may use directional clutches such that the motor direction determines which of the blade sets is powered.

0092Similarly, the blades of the inner tail rotor units <b>308</b> are adapted to stow when in a forward flight configuration, with the blades nested into recesses in the nacelle. The rear tip rotor units <b>305</b> are adapted to rotate relative to the wing such that the nacelle maintains its shape whether in a VTOL or a forward flight configuration. The VTOL blades <b>314</b> are used for VTOL and transition modes, and the forward flight blades <b>311</b> are used for forward flight, with the VTOL blades stowed and nested.

0093In an exemplary configuration of the third embodiment, the aerial vehicle has 12 rotors and weighs 900 kg. The rotor diameter is 1.1 meters, with a thrust per rotor of 736 N. The continuous rpm of the motor at sea level is 1850 rpm, with a maximum of 2270 rpm. The wingspan is 8.9 meters. The battery mass is 320 kg, and the mass per motor is 9 kg. The cruise speed is 320 km/h. The continuous hover power per motor is 19 shaft kW.

0094<figref idref="DRAWINGS">FIGS. 49-52</figref> illustrate a fourth embodiment of an aerial vehicle <b>400</b> in a take-off configuration. A box wing design is seen with the rotor assemblies deployed into vertical take-off configuration.

0095<figref idref="DRAWINGS">FIGS. 53-56</figref> illustrate a fourth embodiment of an aerial vehicle <b>400</b> in a forward flight configuration. As seen the rotor assemblies are rotated into a forward flight configuration. Some of the blades of the rotor assemblies have been stowed to reduce drag in this forward flight mode.

0096In some aspects, aerial vehicles according to embodiments of the present invention take-off from the ground with vertical thrust from rotor assemblies that have deployed into a vertical configuration. As the aerial vehicle begins to gain altitude, the rotor assemblies may begin to be tilted forward in order to begin forward acceleration. As the aerial vehicle gains forward speed, airflow over the wings results in lift, such that the rotors become unnecessary for maintaining altitude using vertical thrust. Once the aerial vehicle has reached sufficient forward speed, some or all of the blades used for providing vertical thrust during take-off may be stowed along their nacelles. The nacelle supporting the rotor assemblies may have recesses such that the blades may nest into the recesses, greatly reducing the drag of the disengaged rotor assemblies.

0097As evident from the above description, a wide variety of embodiments may be configured from the description given herein and additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant's general invention.